A. Technical Field
The present invention relates generally to video processing, and more particularly, to an apparatus and method for in-loop noise reduction within a digital video encoder framework.
B. Background of the Invention
The importance of digital video technology in the current communications markets is well known. The ability to transmit increasing amounts of video data within a constrained bandwidth has allowed the display of video and image content on various devices and platforms. Recent technological advancements within the communications market have facilitated this improvement in the transmission and display of video and image data. One such example is the improvement in coding efficiencies provided by current codec devices and associated standards.
Video data may be encoded in order to reduce the amount of data redundancy that is transmitted within a corresponding digital signal. This reduction in redundant data effectively allows video data to be communicated using relatively less bandwidth. In determining how a video signal is to be encoded, oftentimes an analysis is required of both the video data and the communications medium on which the video data is to be transmitted. This analysis is performed in order to ensure that a preferred video or image quality is maintained on a display device.
The presence of noise within a video signal may adversely affect both the coding efficiency of a codec that is encoding the video signal and the quality of an image or video stream at a receiving display device. Noise may be generated and undesirably inserted into a signal from various internal and external sources. Two such examples of noise are Gaussian noise and impulse noise.
Gaussian noise is often characterized as a uniform distribution of energy having Gaussian distribution levels over a particular frequency spectrum. Gaussian noise may be generated, for example, as temperature increases in communication equipment and devices resulting in thermal noise that is generated and undesirably inserted into a signal. Comparatively, impulse noise is non-continuous noise pulses within the signal. These noise pulses are oftentimes short in duration and have relatively high amplitudes, and may be generated from both internal and external sources.
The presence of noise within a signal may be measured as a signal to noise ratio (“SNR”). As SNR decreases, the quality of a video signal degrades and adversely affects the ability of a display device to regenerate the particular video. This noise may be generated in various locations within a communication system, such as the system illustrated in FIG. 1.
As shown in this Figure, a video capture device, such as a video camera 110, generates a video signal which is sent to an encoder 115. This encoder 115 encodes the video signal, effectively compressing the signal to remove a level of data redundancy. This encoded signal is communicated via a communications link 120, which may be wired or wireless, to a receive-side decoder 125. The decoder 125 reconstructs the encoded video signal so that it may be shown on the display device 130.
The components within this system 100, as well as sources external to the system 100, may generate noise. The presence of noise within a video signal reduces the coding efficiency of the encoder 115 and results in unwanted noise being encoded within the video signal. Various types of noise filters are currently being used to reduce the amount of noise within a video signal including alpha trimmed filters and median filters. Pre-processing noise filters, such as those described in U.S. patent application Ser. Nos. 10/666,668 and 11/261,042, may be employed that remove noise from a video signal prior to the encoder.
These pre-processing filters typically require additional computing resources and may increase the overall complexity of a video coding system. Because these pre-process filters are not influenced by a codec's parameters, the associated filter functions may not be easily adapted based on the codec's settings. Furthermore, these filters often fail to address or leverage certain characteristics of digital video signals when filtering noise.